1. Field of the Invention
This invention pertains to a method for separating a predetermined sheet from an array of sheets on a conveyor.
2. Description of Related Art
Widestock rolls of web, such as film or paper, frequently are cut into sheets suitable for use by a customer, typically by first slitting the wide rolls into narrow rolls and then chopping the film from the narrow rolls into sheets. When the slitting and chopping steps are performed on a widestock roll substantially simultaneously, an array of sheets having transverse rows and longitudinal lanes is transported on a conveyor to a station which stacks the individual sheets for packaging. Typically, in the case where the web is coated, the array of sheets is inspected for defects which occurred during the coating or finishing operation, and defective sheets are separated therefrom. In addition, sheets from the array may be separated for sampling purposes. Furthermore, there may be a desire to randomly combine or shuffle equally sized sheets from different lanes into stacks of sheets which are selected from a variety of different parts of the web. A problem arises when one sheet in the array has a defect or needs to be separated from the array for any purpose. In the past, the entire transverse row or crosscut of sheets containing the defective sheet would be separated. This separating of additional sheets results in much reworking of the separated sheets and possible waste of acceptable, i.e., defect-free, material.
One method which is particularly adapted to handling articles of this nature is to transport the array of sheets by means of a conveyor comprising an endless, perforated belt which moves by means of drive rolls and idler rolls. Typically, such a conveyor includes a vacuum box having an apertured portion about which the perforated belt moves. By this means, the array of sheets that have been positioned on the conveyor will be securely transported by the vacuum from the slitting and chopping location to the stacking location. If the sheets are flexible, limber, or relatively lightweight, such as photographic film sheets, there is a problem when diverting sheets from one vacuum conveyor to another for separating, shuffling, stacking, or special handling, in that a lightweight sheet is easily displaced by air currents, so accurate location of the sheet is difficult to maintain and sheet damage is possible. This is particularly true when the sheet is transported at high speed. There is a need to reliably transfer a single lightweight sheet in an array of sheets from one conveyor to another while continuously retaining positive accurate control of the single sheet and the remainder of the array of sheets.
U.S. Pat. No. 3,500,999 issued to Lippke discloses a sorting and separating system for sheets of material, such as paper or cardboard, that are being transported in transverse rows and longitudinal lanes. The sheets are chopped from a continuous web and are placed on the top of a first air-permeable conveyor below which is a box in communication with a source of suction. In an embodiment shown in FIG. 10 of this patent, good sheets continue to the end of the first conveyor for stacking. Sheets to be separated, such as rejects identified by a checker, are transferred to a second conveyor spaced closely above the first conveyor. Suction to the first and second conveyor boxes can be selectively turned off and on to transfer the sheets upward to the second conveyor, or the sheets can continue along the first conveyor. Sheets can be selectively deposited by the second conveyor into one or more stacks. In another embodiment, the boxes of the conveyors can be alternately subjected to over or under pressure to deposit the sheets. The permeable conveyor belts comprise a screen cloth with metal members for draining off static charge for better sheet handling.
U.S. Pat. No. 3,608,895 issued to Kalven discloses a shuffling and packaging system for flat products, particularly floor tiles. The tiles leave a production conveyor in transverse rows and longitudinal lanes, and are transported by a plurality of conveyors so as to mix the tiles from different lanes for subsequent packaging. The tiles are transported from the production conveyor to an accelerator conveyor. A vacuum conveyor, associated with each lane of tiles, lifts the tiles from the accelerator conveyor and carries the tiles over transverse conveyors. The tiles are selectively deposited onto the transverse conveyors by the operation of unique pressure valves which act to positively break the vacuum supporting the tiles over selected transverse conveyors. The tiles are fully released from the vacuum conveyor so as to drop from the vacuum conveyor to the transverse conveyor from which they are counted and stacked.